This invention relates to automatic transmissions, in which the speed is changed by means of transferring the torque from the transmission shaft similar to the actions of a clutch. The present invention especially concerns the engaging and releasing of the clutch by means of fluid pressure. This is done by means of canceling the original centrifugal hydraulic force in connection with the cancel mechanism.
When there is the appropriate engaging and releasing of the clutch and brake for automatic transmissions, there is a change in the motion of the transmission course in the gear train. This then establishes the plurality of gear stages. For the clutch and brake system in general, the piston is driven by the fluid pressure and engagement is performed by means of the hydraulic servomechanism. For this engaging process, the torque transmission of the clutch and brake system not only meets with resistance, but during the engaging and releasing action, because of the sliding action, it sucks in the used energy and the operation then proceeds with a reduction in shift shock. Therefore reducing the shift shock is an important essential element and is done by means of accurately controling the timing for engaging and releasing the clutch and brake by the hydraulic servomechanism.
The timing for engaging and releasing the clutch and brake system by the hydraulic servomechanism is mostly determined by the degree in the rise and fall of the supply and release of fluid pressure to the hydraulic servomechanism. However, there are times when the hydraulic servomechanism is rotating which makes the expected control of this fluid pressure difficult to achieve.
For engaging the clutch, the hydraulic servomechanism also rotates in the same way. This is because there is a joint that transmits the torque from a part of the rotating input shaft to another rotating part. As the hydraulic servomechanism receives oil, the rotation speed and rotating radius operate by the produced centrifugal force. However, even with the output pressure from the hydraulic servomechanism which should release the clutch, the piston still operates based on the hydraulic pressure from the centrifugal force and the clutch release then becomes slow.
In order to eliminate this unfavourable condition, a check ball valve has been provided inside the piston chamber which receives oil for driving the piston. When it is time to discharge pressure, the check ball valve is opened and the pressure is discharged from the piston chamber.
However, there are times when even the check ball valve does not open so easily due to the centrifugal force. Up until now, many cancel chambers (balance chambers) have been provided to better avoid the effect of the centrifugal hydraulic pressure. One such invention is disclosed in the Japanese Patent laid-open No. 62-52249.
The cancel chamber is employed for eliminating the influence that the centrifugal force has on the piston motion and the engaging and releasing of the clutch. This is done by means of balancing the operational hydraulic chamber which supplies a high pressure fluid for the piston to move the clutch. The high pressure centrifugal fluid pressure chamber is mostly supplied by the balancing of the original operating fluid chamber for the centrifugal force. This produces the pressure and is formed between the piston along with the pressure produced from the centrifugal force in the centrifugal fluid pressure chamber.
Referring to the said cancel chamber, the forward and reverse action of the piston operates along with the increase and decrease of the centrifugal hydraulic chamber. Up until now, an opening was made in the centrifugal fluid chamber coming from the divided fluid passage and traveling along the main fluid passage of the input shaft. The fluid (oil) of the centrifugal hydraulic chamber is discharged or supplied from the fluid passage.
However, in the main fluid passage, even though there are many places where shaft bushes supply fluid, a means to accommodate an equal balance for the changing fluid volume has not been provided for the action of the hydraulic servomechanism. In the cancel mechanism of the prior art, when the volume of the centrifugal fluid pressure chamber greatly increases and the piston returns to the operating hydraulic chamber, the volume of fluid supplied to the centrifugal fluid pressure chamber is not sufficient. The result is that the centrifugal fluid pressure chamber produces an air space and the effective radius quality becomes smaller for the centrifugal fluid pressure chamber.
In the cancel mechanism of the prior art, there has been the problem of an air space being produced inside the centrifugal hydraulic chamber. Then the centrifugal fluid pressure becomes even lower for the operational hydraulic chamber for the so-called produced centrifugal hydraulic pressure. Then the clutch timing for engaging and releasing becomes inappropriate because the effect of the centrifugal force on the piston operation has not completely been eliminated and the shift shock can become very large.